BOGOTA - Soldiers and police raided houses and searched vehicles in Colombia's second city of Medellin yesterday, hunting for Pablo Escobar, police sources said. Escobar, head of the Medellin cocaine cartel, and nine of his lieutenants escaped from prison last week during a bungled military operation to transfer them to another jail.

In Washington, the United States said it had sent military personnel and equipment to Colombia to help in the search for Escobar. A Defense Department spokesman, Pete Williams, said that only a small number of US personnel were involved and stressed that they would not accompany Colombian police in their search for Escobar.

'At the request of the government of Colombia and in accordance with longstanding US policy, the US government is providing support to the Colombians in their efforts to locate Escobar,' Mr Williams said. He refused to specify how many US personnel or what kind of equipment the operation involved, citing concern for the security of the personnel.

Colombian police sources said the security force operations began on Wednesday in several areas of Medellin which Escobar is known to have frequented in the past, including the wealthy suburb of Poblado, and continued yesterday.

Colombian authorities said on Wednesday that US military planes carrying infra-red and other detection devices had overflown a broad sweep of north-western Colombia, including Medellin and Envigado.

It was the first time that Colombian officials had reported the presence of American military planes in the country.

The Colombian army and elite police corps raided properties and set up roadblocks in several areas of the city, where they searched vehicles, the sources said.

Television news said that Envigado, Escobar's home town near Medellin, was virtually under military control. It said police raided homes of several guards who were in charge of security at Escobar's prison, located outside the town.

Police were secretive about the results of the operations. Official spokesmen declined comment and said the President's office was handling all information on the Escobar crisis. Police believe that Escobar has not left the Medellin area.

A new government report, meanwhile, showed that the Bogota government had foreseen the danger that Escobar could escape and ordered extensive security improvements at his jail costing several million dollars. However, the building contractor suspended the work in June after prisoners threatened the workers with death if they continued with the improvements.

Escobar escaped 13 months after surrendering in exchange for President Cesar Gaviria's offer of a lesser jail term.